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Mutations

Mutations. Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”. They can occur at the molecular level (genes) and change a single gene, or at the chromosome level and affect many genes.

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Mutations

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  1. Mutations • Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”. • They can occur at the molecular level (genes) and change a single gene, or at the chromosome level and affect many genes.

  2. Things that can cause mutations are called “mutagens”. • Known mutagens are ultraviolet light, cigarette smoking, certain chemicals like PCB’s.

  3. Effects of Mutations • Silent mutations - have no effect on the expression of the gene. • Causes for this type of mutation: • It is in a non-coding region • It does not change the amino acid sequence • The change does not affect the folding of the protein

  4. Inheritability of Mutations It depends on where it occurs • Germ mutations – occur in gametes. Inheritable (colorblindness, hemophilia) • Somatic mutations – affect body cell, not inheritable (cancer)

  5. Types of Mutations – mistakes • Gene (point) Mutations – effects a single gene i. Substitution ii. Frameshift • Chromosomal mutations – most drastic, change in structure or # of chromosomes (affects many genes)

  6. Point Mutations • Substitution – one base exchanges for another, affects 1 amino acid(Ex. GCA-TCA  GCT-TCA

  7. Mutations 12.4 The Effects of Point Mutations • A point mutation is a change in a single base pair in DNA. • A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein. (SUBSTITUTION) mRNA Normal Protein Stop Replace G with A Point mutation mRNA Protein Stop

  8. Effects of substitution mutations • Missense mutations – causes a change in the amino acid coded for • Nonsense mutations – causes a stop codon to occur prematurely

  9. Frameshift– affects several amino acids -Insertion– 1 base is inserted, affects several amino acids Ex. (GCA-TCA  GCA-GTC-A -Deletion – base is removed, affects several amino acids Ex. (GCA-TCA  GCT-CA

  10. Mutations 12.4 Frameshift Mutations • What would happen if a single base were lost from a DNA strand? • A mutation in which a single base is added or deleted from DNA is called a frameshift mutation because it shifts the reading of codons by one base. • As a result, every codon after the deleted base would be different. Deletion of U mRNA Protein

  11. Chromosome mutations Nondisjunction – incomplete chromosome division during meiosis; results in gametes with too many or too few chromosomes. Ex: Down syndrome is caused by an extra #21 chromosome

  12. Aneuploidy Polyploidy

  13. Down’s Syndrome • Trisomy 21 • 1 in 700 births • Mental retardation • Males are sterile but females are not

  14. Complete the back side

  15. For the lab • Each person needs • A lab sheet • Each group (2 people) needs • A sheet of butcher paper • A DNA sequence (goldenrod) • mRNA nucleotides (multiple colors on the back counter) • tRNA’s (multiple colors on the back right table) • Scissors • Tape • Markers • All other supplies can be found in the beige trays in the back • You will turn in the butcher paper for a grade • The next slide will show you what the butcher paper should look like

  16. Label the following: CODON ANTICODON mRNA DNA Ribosome RNA Polymerase Purine Pyrimidine DNA nucleotide RNA nucleotide Phosphodiester bond Hydrogen bond Peptide bond DNA Strand NUCLEUS CYTOPLASM tRNA’s + amino acid sequence mRNA Strand

  17. Likelihood of chromosomal mutations • 1 in 1700 for mothers < 20. • 1 in 1400 for mothers >20<30. • 1 in 750 for mothers >30<35. • 1 in 16 for mothers >45.

  18. Sex chromosome disorders – occurs as a result of nondisjunction of the sex chromosomes • Ex: Turner’s syndrome – X-; Klinefelter’s syndrome – XXY.

  19. Klinefelter’s Syndrome • XXY • 1 in 1,000 • Usually sterile because of low sperm count • Tall, sparse body hair • Suffer from gynecomastia- male breast tissue • Testosterone treatments

  20. XO genotype—Monosomy X • 1 in 2,500 births • Short, sterile • 75% result in non-disjunction from the father Turner’s Syndrome

  21. Other Chromosomal Mutations • Affect many different genes • Caused by errors in meiosis or environmental disturbances

  22. Translocation – occurs when a piece of one chromosome breaks off and attaches to a nonhomologous chromosome • Inversion – occurs when a piece of one chromosome breaks off, flips, and reattaches to the same chromosome

  23. Deletion – occurs when a piece of a chromosome breaks off and is lost • Duplication – occurs when a segment of a chromosome is repeated

  24. XYY-Jacob’s Syndrome a.k.a. “Super Males” • 1 in 1,000 men • Normal appearance, very tall • Low IQ, prone to violence

  25. 1 out of 6,000 births • Trisomy 13 • 80-90% do not survive past 1 yr old Patau’s Syndrome

  26. Trisomy 18 • Second most common trisomy after down’s syndrome • Only 5% live to age 1 • 1 out of 8,000 births • Severely retarded, many die from malformed heart • Polydactyly or syndactyly Edward’s Syndrome

  27. “ Cry of the Cat” • 1 in 50,000 births • Severe mental retardation • Low mortality rate Cri du Chat

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